Properties of a Sunspot Plume Observed with the Coronal Diagnostic Spectrometer Aboard the Solar and Heliospheric Observatory

摘要

We used three instruments (CDS, EIT, MDI) aboard the Solar and Heliospheric Observatory spacecraft to observe the large sunspot in NOAA Active Region 8539 on 1999 May 9 and 13. The spot contained a bright plume, most easily seen in EUV emission lines formed at 5.2 log T 5.7 (where T is the temperature in K), in its umbra on both dates. The plume's differential emission measure (DEM) exhibited one and only one broad peak, centered around log T ~ 5.8 on May 9 and around log T ~ 5.6 on May 13, and exceeded the DEM of the quiet Sun by more than an order of magnitude at these temperatures. The high-temperature portion of the plume's DEM resembled that of nearby quiet-Sun areas. Intensity ratios of the O IV lines at 625.8 and 554.5 ? yield log ne (where ne is the electron density in cm-3) of 9.6 in the plume on May 9 and 9.7 on May 13; values of 9.4 and 9.4 were obtained in the quiet-Sun areas on the same dates. Based on abundance enhancements derived from transition region emission lines of Ca, an element with low first ionization potential, elemental abundances in the plume appear to be coronal rather than photospheric. The plume plasma reveals a bipolar Doppler velocity flow pattern, in which maximum downflows in excess of 37 km s-1 are observed in the northeast portion of the plume, and maximum upflows that exceed 52 km s-1 are observed in the northwest.